1. Field of the Invention
The present invention relates to a display device including a touch sensor.
2. Description of Related Art
A typical liquid crystal display (“LCD”) includes a pair of substrates provided with pixel electrodes and a common electrode and a liquid crystal layer with dielectric anisotropy interposed between the substrates. The pixel electrodes are typically arranged in a matrix and are connected to switching elements such as thin film transistors (“TFTs”) such that the pixel electrodes receive image data voltages sequentially, row by row.
The common electrode typically covers the entire surface of one of the two substrates and is applied with common voltages. A pixel electrode, a corresponding portion of the common electrode, and a corresponding portion of the liquid crystal layer form a liquid crystal capacitor. The liquid crystal capacitor and a switching element connected thereto form a pixel unit. A plurality of pixel units is typically arranged in a matrix.
An LCD typically generates electric fields by applying voltages to the pixel electrodes and the common electrode and varies the strength of the electric fields in order to adjust the transmittance of light passing through the liquid crystal layer, thereby displaying images.
A touch screen panel is an apparatus on which a finger or a stylus is touched to write characters, to draw pictures, or to instruct a device such as a computer to execute instructions, e.g., by using icons. The touch screen panel has its own mechanism to determine whether or not a touch event exists, and if it does exist, its location on the touch screen panel may also be determined. The touch screen panel is typically attached to a display device such as an LCD. However, an LCD provided with a touch screen panel has a high manufacturing cost due to the cost of the touch screen panel, low productivity due to the additional step for attaching the touch screen panel to the LCD, reduction of the luminance of the LCD and increased thickness of the LCD.
Recently it has been studied that photo sensors have been incorporated on a substrate of an LCD instead of a touch screen panel. A photo sensor has been used to sense the intensity of incident light on a region of the display to give information as to whether or not and where a user's finger or other structure is touching the LCD, e.g., a touch event.
However, the characteristics of photo sensors depend on the uniformity of an amorphous silicon layer of the combined photo sensor and LCD. As a result, there may be errors in the light sensing function, depending on the area being sensed for a touch event. For example, an LCD having the photo sensor may have a malfunction in that it judges a touch that is not actually present as a touch event.